testcast demonstrating rollup getting confused by the presence of "default" as a normal property.

.gitignore

node_modules
dist
package-lock.json

index.js

import * as $protobuf from "protobufjs/minimal";

// This causes the following error:
// [!] Error: Cannot split a chunk that has already been edited (2:58 – "$protobuf.roots["default"]")
// Error: Cannot split a chunk that has already been edited (2:58 – "$protobuf.roots["default"]")
//     at MagicString$1._splitChunk (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:5250:10)
//     at MagicString$1._split (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:5239:51)
//     at MagicString$1.overwrite (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:5052:8)
//     at Node.MemberExpression.render (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:13334:18)
//     at /private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:11347:56
//     at /private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:11215:17
//     at Array.forEach (<anonymous>)
//     at Node.eachChild (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:11207:19)
//     at Node.render (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:11347:14)
//     at Node.MemberExpression.render (/private/tmp/rollup-protobuf-testcase/node_modules/rollup/dist/rollup.js:13339:33)
const $root = $protobuf.roots["default"] || ($protobuf.roots["default"] = {});

export const com = {}

package.json

{
  "name": "rollup-protobuf-testcase",
  "version": "0.0.0",
  "description": "",
  "main": "dist/index.js",
  "module": "dist/index.es.js",
  "jsnext:main": "dist/index.es.js",
  "scripts": {
    "rollup": "rollup -c"
  },
  "license": "UNLICENSED",
  "devDependencies": {
    "protobufjs": "^6.8.4",
    "rollup": "^0.53.3",
    "rollup-plugin-commonjs": "^8.2.6",
    "rollup-plugin-node-resolve": "^3.0.0"
  }
}

rollup.config.js

import commonjs from 'rollup-plugin-commonjs'
import resolve from 'rollup-plugin-node-resolve'
import pkg from './package.json'

export default {
  input: 'index.js',
  output: [
    {
      file: pkg.main,
      format: 'cjs'
    },
    {
      file: pkg.module,
      format: 'es'
    }
  ],
  external: [
  ],
  plugins: [
    resolve(),
    commonjs()
  ]
}